Device for blank pressing optical glass bodies

ABSTRACT

The device for blank pressing glass bodies includes a first rotary indexing table with preforms for forming parisons from glass gobs; a second rotary indexing table having pressing molds and pressing tools for pressing the parisons into final form after formation in the preforms; and a device for shifting the first rotary indexing table relative to the second rotary indexing table so that each preform is positionable in a transfer position between a pressing tool and a pressing mold. Each preform is mounted on the first rotary indexing table by a indexable mount for holding it in a first horizontal position or in a second position pivoted away from the first position, so that, when a preform is in the transfer position, the indexable mount can be pivoted, so that a parison in it drops into the pressing mold for pressing by the pressing tool.

BACKGROUND OF THE INVENTION

The invention relates in the broadest sense to a method for producingblank-pressed glass bodies for optical equipment by preshapingtechnology, in which a single molten glass gob is delivered to alevitation parison mold, and the glass gob, without touching the parisonmold surface, is preformed into a parison, which, after a defined lengthof time has elapsed, is transferred to a separate press mold and ispressed therein into its final form by means of a press tool. To thatend, the parison mold is moved across the press mold for the transfer ofthe glass gob and is stopped in a transfer position and then pivoteddownward, away from the glass gob. The actual invention relates to adevice for blank pressing optical glass bodies, which comprises tworotary indexing tables, of which one has circularly disposed parisonmolds for making the parisons from molten glass gobs, each of which haveextremely tiny openings in their lower region for introducing an aircushion, and the other has circularly disposed press molds for pressingthe parisons after transfer from the parison molds.

It is known to produce glass bodies for the production of opticalequipment, such as lenses, prisms, etc. in highly polished forms, byrepressing re-warmed, blank (fire-polished) glass rods. The re-pressingis necessary to attain the final precise surface optical quality for theglass bodies. In producing some glass bodies, such as aspherical lensesfor automobile headlights, however, the re-pressing operation alone isinsufficient. Milling, grinding and polishing operations are necessaryin addition. In producing blank-pressed condenser lenses, for instance,only the aspherical surface is blank-pressed, while the plane faceopposite the blank face is milled, ground and polished by mechanicaloperations.

The manual re-pressing and the additional method steps that may benecessary dictate a time-consuming, expensive mode of production. Sincethere is a very great need for blank-pressed glass bodies, in particularlenses for automobile headlights, the demand for automatic productiondirectly from the molten phase of the glass, that is, after an in-lineblank pressing process, arises.

This kind of automatic production is possible by means of the preshapingtechnology defined at the outset, which is known for instance fromGerman Patent Disclosure DE-A 24 10 923. The transfer of the glass gobfrom a parison mold is affected according to this reference by placingthe glass gob on a kind of chute along which the parison is guided inthe hot state to a pressing mold. This causes surface defects andchanges of shape, which are currently no longer tolerable. The change inshape furthermore leads in the final analysis to an uneven temperaturedistribution. This too has an adverse effect on shaping in the ensuingpressing operation.

In Japanese Patent Disclosure JP-A 11-157 849, a method of theabove-described kind has been disclosed. In it, the transfer of theglass gob from a parison mold is accomplished by opening the parisonmold and causing the glass gob to drop into a press mold in free fall.This avoids surface defects and changes of shape. However, there is noway to tell how the interaction of the parison mold and the press moldproceeds.

Further methods in this field are known from Japanese Patent DisclosureJP-A 06 206 730 and U.S. Pat. No. 5,762,673.

SUMMARY OF THE INVENTION

Against this background, it is now the object of the present inventionto refine the generic method of the above-described type for pressingoptical glass bodies such that the transfer of the glass gob from theparison mold into the press mold is performed as effectively aspossible. With respect to the device of the above-described type forpressing optical glass bodies, it is the object of the present inventionto refine the device so that transfer of the glass gob from the parisonmold into the press mold is performed as effectively as possible.

According to the invention the device for blank pressing glass bodiesfor optical equipment, such as a lens, by preshaping technology,comprises a first rotary indexing table comprising a plurality oflevitation parison molds in a circular arrangement thereon, each ofwhich comprises means for preshaping a respective molten glass gobdelivered thereto into a corresponding parison and having a lower regionprovided with a plurality of openings for forming an air cushion, sothat the molten glass gob and the parison formed therefrom do notcontact any surfaces of the parison molds;

a second rotary indexing table comprising a plurality of respectivepressing molds and corresponding pressing tools arranged in a circulararrangement thereon, wherein the pressing tools have drive means forpressing the parisons arranged in the pressing molds into a final formafter formation and transfer of the parisons to the pressing molds; and

means for shifting the first rotary indexing table relative to thesecond rotary indexing table so that each parison mold is positionablein a transfer position between a press tool and a press mold after apredetermined time interval for parison formation;

wherein each parison mold is mounted on the first rotary indexing tableby an indexable mount for keeping the respective parison mold associatedwith the corresponding indexable mount in a first horizontal positionfor holding a parison or a second position enabling free fall of theparison, so that, when one of the parison molds is in the transferposition, the indexable mount can be operated to move it from the firsthorizontal position into the second position, whereby the parison heldin it drops into the associated press mold for pressing by itsassociated press tool into its final form.

In a preferred embodiment of the device the first rotary indexing tablemeshes with the second rotary indexing table so that the parison moldscan be moved into their transfer positions by pivoting or rotatablyshifting the first rotary indexing table.

In a further variant, the parison mold preform experiences anacceleration of at least 1 g, that is, the acceleration due to gravity,in executing the pivoting motion. In pictorial terms, the parison moldpreform must be folded away faster than the glass gob or parison movesalong its way in free fall to the pressing mold. As a result, theparison or glass gob reaches the press pressing mold without tilting ofthe parison mold preform.

An embodiment, in which the parison molds preforms are pivotablyconnected to the indexable mounts and can be pivoted downward uponactuation of their actuators, an actuator is especially preferred. Thisembodiment makes the variant method possible in which the parison moldspreforms are pivoted away from the glass gob. The pivoting angle shouldbe at least 90°.

BRIEF DESCRIPTION OF THE DRAWING

The objects, features and advantages of the invention will now beillustrated in more detail with the aid of the following description ofthe preferred embodiments, with reference to the accompanying figures inwhich:

FIG. 1 is a plan view showing the basic arrangement of the two rotaryindexing tables of the device for blank pressing optical glass bodiesaccording to the invention;

FIG. 2 is a diagrammatic side view showing a parison mold the preform inrelation to the press pressing mold prior to the free fall of theparison glass gob; and

FIG. 3 is a diagrammatic side view showing the arrangement of FIG. 2after the free fall of the parison glass gob into the pressing mold.

DETAILED DESCRIPTION OF THE INVENTION

Below, identical reference numerals designate the same elements.

FIG. 1 provides a first overview of the disposition of the variouscomponents. Two cooperating rotary indexing tables 6 and 7 are shown inFIG. 1. They are disposed such that they mesh with one another in atransfer position 8. The first rotary indexing table 6 has the parisonmolds performs 1 arranged in a circle for forming the parisons. Thesecond larger rotary indexing table 7, conversely, has press pressingmolds 2 and press pressing tools 3 arranged in a circle for pressing theparisons. It can be seen that the second rotary indexing table 7 for thepress pressing molds 2 has more positions than the first rotary indexingtable 6 for the parison molds preforms. This is predominantly due to thefact that each pressing die (not shown) of each press pressing tool 3has its own separate drive mechanism. This means that the press pressingtool can be moved simultaneously while the pressing continues. Thuslonger pressing times in proportion to the feeding times are attained bygreater mechanical effort.

FIG. 2 now shows the cooperation of the rotary indexing tables 6 and 7.FIG. 2 shows how after a further cycle, the parison mold preformer hasmoved into the region between the press pressing tool 3 and the presspressing mold 2. The parison mold preform 1 is still located in ahorizontal position on the indexable mount 4.

After a defined length of time, the actuator 5 of the indexable mount 4is actuated, specifically in such a way that the parison mold preform 1is moved into the pivoted-away position, as shown in FIG. 3, with anacceleration that is greater than the acceleration due to gravity. Thepivoting motion causes the glass gob, or parison (not shown), to fallfreely into the press pressing mold 2. The press pressing mold 2 is thenmoved upward. In the process, it presses the parison into the finalproduct.

1. A device for performing a process for producing blank-pressed glassbodies for optical equipment according to preshaping technology, saidprocess comprising feeding a molten glass gob to a levitation parisonmold (1), preshaping the glass gob to form a parison without touchingany surface of the parison mold (1), transferring the parison to aseparate press mold (2), and pressing the parison to a final form in thepress mold (2) with a press tool (3) adapted for pressing the parison inthe press mold, said transferring taking place so that said parisonfreely drops from the parison mold (1) into the press mold (2) bypositioning the parison mold (1) over the press mold (2) in a transferposition and then pivoting the parison mold (1) downward and away fromthe parison; said device comprising two rotary indexing tables (6, 7),one of which has a plurality of parison molds (1) in a circulararrangement thereon, each of which are provided with openings in a lowerregion thereof through which air is fed to form an air cushion forlevitating the glass gob and the parison formed therefrom, and anotherof which has a plurality of press molds (2) in a circular arrangementthereon and a plurality of press tools (3) arranged to cooperate withsaid press molds to form said blank-pressed glass bodies; in which saidparison molds (1) are held in said one of said two indexing tables (6,7) by indexable mounts (4), each of which is switchable between ahorizontal position in which one of said parison molds (1) is held insaid horizontal position over one of the press molds (2) and anotherposition in which the parison held in said one of said parison moldsfreely drops into an associated one of the press molds (2) of saidanother of said two indexing tables (6, 7).
 2. The device as defined inclaim 1, wherein the indexable mounts (4) comprise actuators (5) forpivoting the parison molds (1) downward and away from the horizontalposition to said another position.
 3. The device as defined in claim 2,wherein the actuators (5) comprise means for pivoting the parison moldsthrough a pivoting angle of at least 90°.
 4. The device as defined inclaim 2, wherein said parison mold (1) experiences an acceleration of atleast 1 g during said downwardly pivoting.
 5. A device forblank-pressing glass bodies for optical equipment according topreshaping technology, said device comprising a first rotary indexingtable (6) comprising a plurality of levitation parison molds (1) in acircular arrangement thereon, each of said levitation parison molds (1)comprising means for molding a respective molten glass gob suppliedthereto into a corresponding parison and having a lower region providedwith a plurality of openings for forming an air cushion so that saidmolten glass gob and said parison formed therefrom do not contact anyparison mold surfaces; and a second rotary indexing table (7) comprisinga plurality of respective press molds (2) and corresponding press tools(3) arranged in a circular arrangement thereon, each of said press tools(3) being adapted to cooperate with an associated one of said respectivepress molds (2) for pressing said parison into a final form afterformation and transfer of said parison thereto; in which said firstrotary indexing table (6) meshes with said second rotary indexing table(7) and is moveable relative to said second rotary indexing table (7)into at least one transfer position (8) in which one of said parisonmolds (1) is positioned between one of said press tools (3) and saidassociated one of said press molds (2); and in which said one of saidparison molds (1) is pivotably mounted on the first rotary indexingtable (6) on a respective indexable mount (4) provided with an actuator(5) for pivoting said one of said parison molds (1), so that, when saidfirst rotary indexing table (6) is in said at least one transferposition (8), said one of said parison molds (1) is pivotable by saidactuator from a horizontal position in which said parison is held insaid one of said parison molds (1) downward to a downwardly pivotedposition in which said one of said parison molds is no longer positionedbetween said one of said press molds (2) and said one of said presstools (3) so that during the pivoting of said one of said parison molds(1) said parison held in said one of said parison molds (1) drops infree fall into said one of said press mold (2) for pressing into saidfinal form by said one of said press tools (3).
 6. The device as definedin claim 5, wherein said one of said parison molds (1) is pivoteddownward from the horizontal position to the downwardly pivoted positionthrough an angle of at least 90°.
 7. The device as defined in claim 5,wherein said one of said parison molds (1) experiences an accelerationof at least one g when moved between said horizontal position and saiddownwardly pivoted position enabling said free fall.